Alumina (aluminium oxide; Al2O3) has been used in structural components such as heat engines and other applications requiring good oxidation, corrosion resistance and high wear resistance. However, the low toughness and brittle failure mode of monolithic alumina significantly reduces the reliability of the material during use.
Efforts to improve the mechanical properties of monolithic alumina have been the focus of attention of engineers and ceramic researchers for many years. As a result, a number of different approaches have been proposed in this area. Of these, the use of second phase reinforcements has been one of the most successful approaches. The second phase can play an important role, such as providing obstacles that can divert a propagating crack or act as bridging elements, thus increasing the crack resistance and flexure strength of the material. It has been found that the properties of alumina may be enhanced by incorporating a fine dispersion of a second ceramic phase throughout the material.
In particular, it has been found that the inclusion of a second phase comprising silicon carbide (SiC) nanoparticles may improve the wear resistance and surface finish of alumina. The silicon carbide nanoparticles cause the fracture mode of the material to change from intergranular to transgranular. The silicon carbide-containing materials have significantly improved wear resistance compared with monolithic alumina. According to Ortiz-Merino et al (Acta Mater., 53, 3345-57), the addition of only 2 vol % silicon carbide improves wear properties by a decrease in the number of pullouts and also a reduction in pullout size, both resulting mainly from the change in fracture mode.
Despite having commercially desirable properties, the cost of the silicon carbide nanopowders means that the materials may be significantly more expensive to produce than alumina. Moreover, the green compacts are usually sintered at relatively high temperature and pressure. This can add further expense and can limit the ability to produce large or complicated parts.